Oil Flow to front oil cooler/thermostat

[Bb5280]

Have a 72 frame/body (with oil tank behind passenger door) and a 74 2.7 case. Previous owner did all work (and now I am at the end of a complete rebuild). Need to see if this is right - I don't think so but thought others would have more expertise. If you look at the picture with the thermostat - the back line comes from filter on the left, in to therm, then out to front oil cooler - that seems fine to me. The return from the oil cooler comes back, loops around and then comes in the the thermostat from the left and then in to the tank. Maybe it is the Mocal therm and it operates different but intuition tells me it should come back to the therm from the right side of the therm and then the line leaving therm to left should loop to the tank. The diagram picture shows what is on the top and what seems right to me on the bottom. Does the Mocal therm work the same as all others - ---> on the "top" and <---- on the bottom?

[dyerkes]

Refer to the following post for a diagram of the oil flow Ultimate Oil Pressure Relief Valve Thread

Regards,
David

[stownsen914]

I didn’t see anything about the Mocal thermostat in that thread, but I might have missed it.

I have the Mocal thermostat on two different cars, and initially was confused by the recommended routing. It operates differently than a factory thermostat. The Mocal does not positively redirect flow when it opens/closes. In the “cold” position, there is a bypass that opens to allow flow from the pre-cooler line to the post-cooler line. There is a diagram that Mocal makes to show the correct routing. Maybe google it or give Mocal or one of their distributors a call.

Scott

[stownsen914]

Just googled “Mocal thermostat diagram” and found it.

[ossiblue]

From what I could see on the Mocal diagram, your thermostat is plumbed incorrectly. As you speculate, the return from the cooler should be connected to the front port (cooler side) of the thermostat, not looped around to the engine side.

Here's a diagram of the thermostat when in operation:



If you connect the return line to the engine side of the thermostat, then, when the thermostat is closed, the cold oil will circulate up to the cooler and be stopped back at the thermostat. The possibility then arises that high, cold oil pressure, could damage the cooler.

Look at the left side diagram and imagine the cold oil entering the thermostat at the top, left port, exiting through the bottom left port, flowing up to the cooler and returning to the upper right port where it stops. Not only will you build pressure in the cooler, but the flow through the cooler will be reversed as well, something you may not wish to happen.

[stownsen914]

I wasn’t following your diagram at first, but actually I think you may have it right. If you are asking whether the direction of flow of oil coming back from the cooler and through the Mocal thermostat matters, it doesn’t actually. This may not be intuitive, but for this type of thermostat it doesn’t affect the operation.

To confirm, “from filter” in your case is scavenge oil from the engine?

Also, one thing to note in the Mocal diagram is that return to engine for a 911 (dry sump) is actually to the tank.

Scott

[Bb5280]

Originally Posted by stownsen914

I wasn’t following your diagram at first, but actually I think you may have it right. If you are asking whether the direction of flow of oil coming back from the cooler and through the Mocal thermostat matters, it doesn’t actually. This may not be intuitive, but for this type of thermostat it doesn’t affect the operation.

To confirm, “from filter” in your case is scavenge oil from the engine?

Also, one thing to note in the Mocal diagram is that return to engine for a 911 (dry sump) is actually to the tank.

Scott

Thanks Scott - yes, the oil is coming from the engine, through the filter mounted in the passenger rear. The therm you see is in the passenger rear wheelwell. if the Mocal therm operates like the diagram, then the way it is currently plumbed, when cold, the therm would be sending to the front cooler. When hot, it would again send to the front cooler, but the return would be OK because both sides would be open? Is that what you are refering to when you say it may not be intuitive. Still does not eliminate that when cold, it should be going straight to the tank and not the front cooler. I wish I was better at graphics so I could write on this picture -

[ossiblue]

Originally Posted by stownsen914

I wasn’t following your diagram at first, but actually I think you may have it right. If you are asking whether the direction of flow of oil coming back from the cooler and through the Mocal thermostat matters, it doesn’t actually. This may not be intuitive, but for this type of thermostat it doesn’t affect the operation.

To confirm, “from filter” in your case is scavenge oil from the engine?

Also, one thing to note in the Mocal diagram is that return to engine for a 911 (dry sump) is actually to the tank.

Scott

Okay, maybe I'm missing something here.

The flow through the Mocal will affect the operation of the thermostat and it disrupts the correct oil flow of the 911 system. Look at the two diagrams I posted showing the Mocal in the closed and open positions. Let's substitute the word "Tank" for the word "Engine" for the destination of the return port. Now, mentally connect the front cooler to the ports as described by the OP.

If the Mocal is plumbed like the OP describes with the return from the cooler connected to the left, lower port, how does the oil get back to the tank when the thermostat is closed? There is no access for the oil to enter the tank through the Mocal internal drillings, from the top right port (where the oil is now stopped) to the bottom right port where the line to the tank is connected. There is no oil flow back into the tank, and, more importantly, there is no oil flow through the thermostat either. Without oil flow through the thermostat, it will take longer for it to warm up and open. As it is plumbed now, the warm up has to come from "radiant" heating of the stationary oil trapped in the body of the thermostat. A factory external thermostat allows oil to flow through it, when closed, and as the flowing oil heats up the thermostat opens.

If plumbed correctly, the Mocal would do the same. Cold oil would by-pass the cooler, but would be circulating through the thermostat all the while. As the circulating oil heats, the thermostat will open sooner and oil will flow to the cooler.

Again, maybe I'm missing something, but the diagram supplied by the OP which shows the return from the cooler entering the "engine" side of the thermostat and exiting to the tank via the "cooler" port, ought to be corrected, IMO.

[Bb5280]

ok - as best I could with my rudimentary skills - here is how it is plumbed - I can not believe this is correct. When cold, the therm would route the cold oil into what is plumbed as the return from the FOC. From this diagram, unless I am misunderstanding how the MOCAL therm works, cold oil would never flow striaght to the tank -

[Bb5280]

[ossiblue]

Originally Posted by Bb5280

I agree, it is not correct. The top two lines should be switched, IMO, to have the thermostat plumbed as designed.

[Bb5280]

Originally Posted by ossiblue

Okay, maybe I'm missing something here.

The flow through the Mocal will affect the operation of the thermostat and it disrupts the correct oil flow of the 911 system. Look at the two diagrams I posted showing the Mocal in the closed and open positions. Let's substitute the word "Tank" for the word "Engine" for the destination of the return port. Now, mentally connect the front cooler to the ports as described by the OP.

If the Mocal is plumbed like the OP describes with the return from the cooler connected to the left, lower port, how does the oil get back to the tank when the thermostat is closed? There is no access for the oil to enter the tank through the Mocal internal drillings, from the top right port (where the oil is now stopped) to the bottom right port where the line to the tank is connected. There is no oil flow back into the tank, and, more importantly, there is no oil flow through the thermostat either. Without oil flow through the thermostat, it will take longer for it to warm up and open. As it is plumbed now, the warm up has to come from "radiant" heating of the stationary oil trapped in the body of the thermostat. A factory external thermostat allows oil to flow through it, when closed, and as the flowing oil heats up the thermostat opens.

If plumbed correctly, the Mocal would do the same. Cold oil would by-pass the cooler, but would be circulating through the thermostat all the while. As the circulating oil heats, the thermostat will open sooner and oil will flow to the cooler.

Again, maybe I'm missing something, but the diagram supplied by the OP which shows the return from the cooler entering the "engine" side of the thermostat and exiting to the tank via the "cooler" port, ought to be corrected, IMO.

I have to agree with you - I wasn't sure if the MOCAL did something different or not - - but it just did not look right to me - had an engine failure and was looking at the lines and getting new and that setup just looked wrong as I traced it out.

[stownsen914]

You guys are getting confused about how the Mocal thermostat works. No insult intended here - I was too when I first bought one. I had to call the dealer to explain how it worked because even holding it in my hand, it didn't make sense to me.

The key thing is that the thermostat doesn't work by positively blocking flow to the cooler when in the "cold" position. It only gives an alternate path (the bypass) for oil to go when cold. The oil follows the path of least resistance and more of it goes back to the tank than through the cooler due to the natural extra resistance of the cooler path. Then once warm, the bypass shuts, and oil can only flow through the "straight line" paths - engine/filter to cooler, and then cooler back to engine/tank.

The key thing with the Mocal is to have a straight path through the thermostat from the engine (filter in this case) to the cooler, and also a straight path through the Mocal from the cooler back to the engine/tank. Don't be misled into thinking the diagram is saying that flow through the bypass has to do that 180 turn for the thermostat to work correctly. It just has to flow from one side of the thermostat to the other.

I'll try to draw up a couple diagrams to show you what I mean.

Or just call Mocal if you'd prefer a real expert opinion .

Scott

[stownsen914]

OK, here is my attempt to illustrate the hot and cold flow paths for the Mocal thermostat in the OP's configuration.

First up is the hot path. The paths are indicated by the arrows. Filter/engine to cooler, and cooler to tank. The bypass is blocked when warm, indicated by the red X.





Cold path - the bypass is open now. The regular straight paths are still unrestricted. The green arrow indicates the path for the OP's case when cold, instead of the 180 degree turn shown in the Mocal diagram. Nothing is blocked off when the thermostat is in the cold position. The only difference is the bypass is open, providing the "least resistance" path for the oil to follow back to the tank instead of going through the cooler. Mocal explained that some flow still does happen through the cooler when the bypass is open, but much less.

[ossiblue]

Originally Posted by stownsen914

OK, here is my attempt to illustrate the hot and cold flow paths for the Mocal thermostat in the OP's configuration.

First up is the hot path. The paths are indicated by the arrows. Filter/engine to cooler, and cooler to tank. The bypass is blocked when warm, indicated by the red X.





Cold path - the bypass is open now. The regular straight paths are still unrestricted. The green arrow indicates the path for the OP's case when cold, instead of the 180 degree turn shown in the Mocal diagram. Nothing is blocked off when the thermostat is in the cold position. The only difference is the bypass is open, providing the "least resistance" path for the oil to follow back to the tank instead of going through the cooler. Mocal explained that some flow still does happen through the cooler when the bypass is open, but much less.

Okay, that does make sense given the thermostat does not completely shut off the flow from the cooler.

[Zaz]

See/zoom attached

[Zaz]

Correct 2nd page/pic below